Black hole-naked singularity dualism and the repulsion of two Kerr black holes due to spin-spin interaction

We report about the possibility for interacting Kerr sources to exist in two different states - black holes or naked singularities - both states characterized by the same masses and angular momenta. Another surprising discovery reported by us is that in spite of the absence of balance between two Kerr black holes, the latter nevertheless can repel each other, which provides a good opportunity for experimental detection of the spin-spin repulsive force through the observation of astrophysical black-hole binaries. (c) 2019 The Authors. Published by Elsevier B.V.